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Understanding the Endocrine System (mod 7)
Oct 15, 2024
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Lecture Notes: Chapter 17 - The Endocrine System
Overview
Transition from the nervous system to the endocrine system.
Focus on the integration between the nervous system and the endocrine system.
Endocrine System
Composed of glands or glandular structures.
Secretes hormones into the bloodstream (endocrine glands) as opposed to exocrine glands, which secrete externally.
Hormones are chemical messengers.
Communication in the Body
Nervous System: Uses electrical signals via neurons for fast communication.
Endocrine System: Uses hormones for communication, influencing distant tissues through the bloodstream.
Modes of Chemical Signaling
Direct Communication
: Cells directly adhere and share cytoplasm through gap junctions.
Paracrine Communication
: Local communication through extracellular fluid; involves paracrine factors.
Endocrine Communication
: Hormones travel through the bloodstream to distant target cells.
Synaptic Communication
: Neurotransmitters cross synapses between neurons.
Autocrine Communication
: Cells respond to their own secretions.
Nervous vs. Endocrine Systems
Speed
: Nervous is fast; endocrine is slow due to hormone circulation.
Duration
: Nervous has short impacts; endocrine has long-lasting effects.
Modulation
: Nervous uses frequency modulation; endocrine uses amplitude modulation.
Impacts
: Nervous impacts are specific; endocrine impacts are widespread.
Hormone Structural Categories
Amino Acid Derivatives
: Modified amino acids (e.g., tyrosine, tryptophan).
Examples: Thyroxine, catecholamines, melatonin.
Peptide Hormones
: Chains of amino acids (e.g., glycoproteins, small proteins).
Examples: Insulin, growth hormone.
Lipid Derivatives
: Derived from lipids (e.g., eicosanoids, steroids).
Examples: Testosterone, estrogen, prostaglandins.
Hormone Solubility
Polar (water-soluble) hormones bind to membrane receptors.
Nonpolar (lipid-soluble) hormones can cross membranes directly.
Hormone Circulation
Freely Circulating
: Rare, quick removal; half-life ~30 minutes.
Bound to Plasma Proteins
: Common, longer half-life (days/weeks).
Patterns of Hormone Secretion
Chronic Secretion
: Constant rate of release (e.g., thyroid hormones).
Acute Secretion
: Released in response to stimuli (e.g., insulin).
Episodic Secretion
: Occurs at specific intervals (e.g., menstrual hormones).
Control of Hormone Secretion
Humoral
: Response to local conditions (paracrine factors).
Neural
: Direct stimulation by the nervous system.
Hormonal
: Controlled by other hormones (hormone pathways).
Hormone Pathways
Releasing Hormones
: From hypothalamus, trigger tropic hormones.
Tropic Hormones
: From anterior pituitary, stimulate other glands.
Terminal Hormones
: Produced by target endocrine glands.
G Protein and Second Messengers
Membrane-Bound Receptors
: Use G proteins to activate intracellular pathways.
Second Messengers
: Cyclic AMP or calcium/calmodulin complexes.
Intracellular Receptor Binding
: Nonpolar hormones bind to internal receptors affecting gene expression.
Hormone Action on Cells
Steroid Hormones
: Directly enter cells and impact gene expression.
Thyroid Hormones
: Transported into cells, alter metabolism and gene expression.
Summary
The endocrine system provides long-lasting and widespread modulation of body processes through hormones.
Understanding hormone pathways and the interplay between different systems is critical for comprehending body regulation.
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